Automotive vehicles commonly employ a port-injected internal combustion engine in which a fuel injector sprays fuel into an intake manifold of the engine near an intake valve of a cylinder. A conventional fuel injector is typically controlled in response to a fuel injection pulsewidth signal where the pulsewidth determines the amount of fuel injected into the corresponding cylinder of the engine. The fuel injection pulsewidth signal may be based on a calculated target fuel injection mass, where the goal of the calculated target fuel injection mass is to provide adequate engine performance when post combustion sensor feedback-based engine control is not available.
Many automotive vehicles commonly employ an oxygen sensor generally disposed upstream of the catalyst system for sensing the oxygen level in the exhaust gas emitted from the engine. The oxygen sensor can serve to provide a feedback signal to control engine operation and adjust fuel injection to the engine to achieve good engine performance. However, some conventional oxygen sensors are required to warm up to a sufficiently high temperature before an accurate oxygen sensor reading may be obtained. Also, following an engine start, the oxygen sensor and processing devices often have not acquired enough information to provide adequate feedback control. Therefore, for a period of time immediately following start-up of the engine, the oxygen sensor may not be capable of providing accurate information with which the engine may be accurately controlled to achieve low hydrocarbon emissions. As a consequence, excessive hydrocarbon emissions may be emitted from the vehicle within the immediate period following start-up of the engine.
Additionally, immediately following an engine start, the catalytic converter can be ineffective since the catalyst requires a period of time to warm up to a temperature at which the catalyst can operate effectively to oxidize excess hydrocarbons. As a consequence, exhaust tailpipe hydrocarbon emissions may initially be high due to poor burning of the excess hydrocarbons. To add to the problem, an overabundance of hydrocarbons in the catalyst may further cool the catalyst, thereby requiring an extended period of time for the catalyst to function efficiently.
Evaluation of combustion performance of an engine may be used to improve engine control and to evaluate hardware changes made to the engine. One metric, combustion stability, can be measured by processing engine speed signals taken over an angular displacement of the expansion stoke of the engine cylinders. By computing a level of engine roughness, engine operation may be controlled while other feedback is unavailable, for example, when the oxygen sensor is too cold. However, in hybrid vehicles, an electric motor often controls the speed of the combustion engine making engine stability and roughness measurements hard or impossible to obtain because the electric motor is controlled faster than the combustion engine, especially at lower engine speeds. Accordingly, there is a need for improvements in the fuel control system of a hybrid vehicle to allow for computation of engine roughness, or some equivalent measure, to modify fuel injection so as to improve fuel economy and hydrocarbon emissions while maintaining adequate performance of the vehicle.